1. Field of the Invention
The present invention relates to papermakers felts in general, and to a papermakers wet felt having a smooth paper-receiving surface and a ribbed machine roll contacting surface.
2. Background of the Prior Art
Ideally, a papermakers wet felt should comprise an endless belt having a smooth paper-receiving surface for importing a smooth finish to a paper sheet that is being transported thereon, and an abrasive resistant machine roll contacting surface for draining water from the paper sheet and for coacting with the machine roll to advance the paper sheet to the next stage in the papermaking process. Because of the high speeds and tremendous roll pressures developed by today's papermaking machines there is a tendency for papermakers wet felts to mark the paper sheets as they pass through the nip of a machine press and to wear excessively on the roll contacting surface as it passes over the machine rolls, suction boxes, and other machine elements.
Originally, papermakers wet felts were made of a woven cloth, having a woolen spun yarn in both the machine direction and the cross machine direction. As the speed of paper production increased, such cloths were found to be inadequate. Performance of the original woven cloth papermakers felt was greatly improved through the inclusion of synthetic fibers in the spun yarns. Subsequently, improvements included the emergence of batt-on-base felts, where a fibrous batt or fleece composed of non-woven fibers is needled to a woven base cloth. This development was followed by the batt-on-mesh felt, where essentially the same fabric is produced but the base cloth is non-compressible. A preferred method of producing the non-compressibility in the base cloth is to use resin impregnated, plied multifilament yarns in both the machine direction and the cross machine direction or to use monofilament yarns for the cross machine direction and machine direction threads. The non-compressibility of the base cloth provides void areas which accept water from the paper sheet as it passes through the nip of the paper machine press and transports the water forward to a suction box for removal. However, because the base cloth is resin treated for stiffness rather than strength, there is still a problem of abrasion wear against the machine rolls. In addition, a complex weaving structure is needed to generate a base cloth having the necessary void areas coupled with the proper rib structure for machine roll contact.
It has been found that a batt-on-mesh felt, which has batt fiber added only to the paper receiving surface of the felt, will provide better water removal on the paper machine than a felt which has batt added to both the paper-receiving surface and the roll contacting surface of the papermakers felt.
A papermakers felt, as used in the papermaking process, must receive, transport and remove water. At the same time the felt must provide a smooth paper receiving surface in order to produce a paper which does not suffer from marking problems. Further, the felt must also act to support the paper, while at the same time facilitating draining.
It has been observed that the prior art papermakers felts suffer from one or more of the following problems: excessive wear of the felt on the machine roll surface, paper marking problems, inadequate drainage capabilities, and premature belt failure.
There is thus a need for an improved wet felt which minimizes the problems associated with the prior art felts. The present invention is directed toward filling that need by providing a composite cloth having a smooth paper-receiving layer of non-woven batting material, an intermediate woven layer of synthetic yarns to impart strength to the felt while also providing void areas for drainage, and a bottom woven layer of ribbed construction to provide an abrasion resistant machine element contacting surface and a superior drainage structure.